1. Field of the Invention
The present invention relates to an improved dissolved oxygen electrode for measuring a concentration of oxygen in a sample liquid and, more particularly, to a verification system to monitor its operability during use.
2. Description of Related Art
Conventional galvanic cell-type dissolved oxygen electrodes are frequently utilized to measure a concentration of oxygen in various sample liquids. A partial cross-sectional view of such a dissolved oxygen electrode is shown in FIG. 2.
A housing substrate 1 can be made of an insulating material, such as a synthetic resin, that will be inert to the fluids that it will encounter. The housing 1 can be formed into a cylindrical lower half portion having a central annular groove 1b that extends about an axial core portion 1a. The core portion 1a integrally extends from a central portion of the cylindrical lower half portion and is capable of supporting, for example, an annular anode 2 located on its outer circumferential surface. This anode 2 is connected with an appropriate terminal wire 6 that can extend outside of the housing 1 through a lead wire 4 arranged within the housing 1. An additional lead wire 5 is connected to another terminal 7 located outside of the housing 1, and extends to the lower tip of the axial core portion 1a. Cathode 3 can be mounted within a recess in the core portion 1a and connected to the lead wire 5 at this location. The entire lower end of the housing substrate 1 is covered with a diaphragm 8, of a known construction, that is permeable to oxygen. The inner hollow portion is thus formed between the diaphragm 8 and the annular groove 1b of the housing substrate 1. An appropriate electrolyte 9 can be sealed within this hollow portion 1b.
The dissolved oxygen electrode, when immersed in a sample liquid, can have oxygen from the sample liquid transmitted through the diaphragm 8, and subsequently be electrochemically reduced on a surface of the anode 2. This reaction will produce an electric current proportional to the concentration of oxygen in the sample liquid between the anode 2 and the cathode 3 through the electrolyte 9, which can be conveniently measured across the respective terminals 6 and 7 to provide a measurement signal proportional to the concentration of oxygen in the sample liquid.
If, during the use of the dissolved oxygen electrode, the diaphragm 8 becomes damaged, then the electrolyte 9 can either flow out of the housing 1 through the damaged portion of the diaphragm 8, or sample liquid can flow into the inner hollow portion 1b of the housing 1, to correspondingly contaminate the electrolyte 9. As a result, a value of electric current flowing between the anode 2 and the cathode 3 will be affected and will be generally reduced. In a conventional dissolved oxygen electrode, any damage to the diaphragm 8 may not be easily confirmed, so that a problem has frequently occurred in that the concentration of oxygen being measured will become erroneous since the operator may not know that there has been damage to the diaphragm 8. Additionally, the degree of damage to the diaphragm 8 may be progressive, and the resulting accuracy of the reading may also progressively deteriorate without being detected by the technician.
Efforts in the prior art to determine any damage to the diaphragm 8 have usually resulted from an estimate of the reduction of value of the electric current, but this generally required the necessity of specifying a sufficient reduction of the value of the electric current so that it would be observed as being outside of the range of the expected measurement. It may also require a testing procedure wherein the conventional dissolved oxygen electrode can be immersed in a specified sample, such as the atmosphere and a precalibrated saturate dissolved oxygen solution, in order to measure the value of the electric current. This calibration or testing procedure can be troublesome and can require the interruption of the actual measurement cycle of the dissolved oxygen electrode.
An additional problem occurs in that a reduction in the measured electric current can also occur as a result of a simple deterioration in the useful lifetime of both the anode 2 and the cathode 3. It is not always possible to determine if there has been damage to the diaphragm 8 or if the life cycle of the anode 2 and cathode 3 has been simply reduced through normal usage.
Thus, there is a demand in the prior art to provide an easy and economical verification system to determine the reliability of a dissolved oxygen electrode.